This invention relates to the compositions of matter useful as catalysts, to a method for preparing these catalysts and to a method for polymerization utilizing the catalysts.
The use of soluble Ziegler-Natta type catalysts in the polymerization of olefins is well known in the prior art. In general, such systems include a Group IV-B metal compound and a metal or metalloid alkyl cocatalyst, such as aluminum alkyl cocatalyst. More broadly, it may be said to include a mixture of a Group I-III metal alkyl and a transition metal complex from Group IVB-VB metals, particularly titanium, zirconium, or hafnium with aluminum alkyl cocatalysts.
First generation cocatalyst systems for homogeneous metallocene Ziegler-Natta olefin polymerization, alkylaluminum chlorides (AlR2Cl), exhibit low ethylene polymerization activity levels and no propylene polymerization activity. Second generation cocatalyst systems, utilizing methyl aluminoxane (MAO), raise activities by several orders of magnitude. In practice however, a large stoichiometric excess of MAO over catalyst ranging from several hundred to ten thousand must be employed to have good activities and stereoselectivities. Moreover, it has not been possible to isolate characterizable metallocene active species using MAO. The third generation of cocatalyst, B(C6F5)3, proves to be far more efficient while utilizing a 1:1 catalyst-cocatalyst ratio. Although active catalyst species generated with B(C6F5)3, are isolable and characterizable, the anion MeB(C6F5)3xe2x8ax96, formed after Mexe2x8ax96 abstraction from metallocene dimethyl complexes is weakly coordinated to the electron-deficient metal center, thus resulting in a drop of certain catalytic activities. The recently developed B(C6F5)4xe2x8ax96 type of non-coordinating anion exhibits some of the highest reported catalytic activities, but such catalysts have proven difficult to obtain in the pure state due to poor thermal stability and poor crystallizability, which is crucial for long-lived catalysts and for understanding the role of true catalytic species in the catalysis for the future catalyst design. Synthetically, it also takes two more steps to prepare such an anion than for the neutral organo-Lewis acid.
Accordingly, it is an object of the subject invention to prepare and utilize a new class of olefin polymerization catalysts.
A further object of the subject invention is a catalyst which permits better control over molecular weight, molecular distribution, stereoselectivity, and comonomer incorporation.
Another object of the subject invention is a Ziegler-Natta type catalyst system which reduces the use of excess cocatalyst and activates previously unresponsive metallocenes.
These and other objects are attained by the subject invention whereby in one embodiment, a strong organo-Lewis acid, such as perfluorobiphenylborane (PBB) is utilized as a highly efficient cocatalyst for metallocene-mediated olefin polymerization and as a catalyst for a ring opening polymerization of THF. PBB can be synthesized in much higher yield than B(C6F5)3 and the anion generated with PBB is non-coordinating instead of weakly coordinating as in the case of B(C6F5)3. Thus, the former exhibits higher catalytic activities and can activate previously unresponsive metallocenes. The catalytically active species generated with PBB are isolable, X-ray crystallographically characterizable instead of the unstable, oily residues often resulting in the case of B(C6F5)4xe2x8ax96. In addition, PBB exhibits even higher catalytic activities in most cases.
In one embodiment of the subject invention a strong organo-Lewis acid, such as perfluorobiphenylborane (PBB), is utilized to synthesize stoichiometrically precise, isolable/crystallographically characterizable, highly active xe2x80x9ccation-likexe2x80x9d metallocene polymerization catalysts. The biphenyl groups of PBB may be connected to the boron at the meta, para, or ortho position.
PBB reacts with early transition metal or actinide alkyls to yield highly reactive cationic complexes: (CpCpxe2x80x2MR)⊕(RBRxe2x80x2Rxe2x80x32)xe2x8ax96
where
CpCpxe2x80x2=C5HnR5-n(n is 0-5), indenyl, allyl, benzyl, C5HnR4-nXNR (n is 0-4);
M=early transition metal or actinide, e.g., Ti, Zr, Hf, Th, U;
X=Rxe2x80x2xe2x80x32Si, where Rxe2x80x2xe2x80x3 is an alkyl or aryl group (Cxe2x89xa610);
R, Rxe2x80x2xe2x80x3=alkyl, benzyl, or aryl group (Cxe2x89xa620), hydride, silyl;
B=boron
Rxe2x80x2=fluorinated biphenyl
Rxe2x80x3=fluorinated phenyl, fluorinated biphenyl, or fluorinated polycyclic fused rings such as naphthyl, anthracenyl, or fluorenyl.
As a specific example of the above, the reaction of PBB with a variety of zirconocene dimethyl complexes proceeds rapidly and quantitatively to yield, after recrystallization from hydrocarbon solvents, the catalytic complex of Eq. 1. 
Such catalytic complexes have been found to be active homogeneous catalysts for xcex1-olefin polymerization and, more particularly, the polymerization, copolymerization or oligopolymerization of ethylene, xcex1-olefins, dienes and acetylenic monomers, as well as intramolecular Cxe2x80x94H activation.
The cocatalyst of the subject invention may be referred to as BRxe2x80x2Rxe2x80x32, where B=boron; Rxe2x80x2 and Rxe2x80x3 represent at least one and maybe more fluorinated biphenyls or other polycyclic groups, such as naphthyl. Two of the biphenyls may be substituted with a phenyl group. Both the biphenyls and the phenyl groups should be highly fluorinated, preferably with only one or two hydrogens on a group, and most preferably, as in PBB with no hydrogens and all fluorines.